Officer Warren Lee hands in a gun turned over by a citizen at a gun buy back program in the Mission in San Francisco, Calif., Thursday, August 8, 2013. Guns were exchanged for $100, assault weapons for $200 -- no questions asked. The program was funded by San Francisco Supervisor David Campos' discretionary fund and GunbyGun.org which crowd sourced the money.

Photo: Sarah Rice, Special To The Chronicle

Officer Warren Lee hands in a gun turned over by a citizen at a gun...

Officer Warren Lee hands in a gun turned over by a citizen at a gun... Photo-5021050.67888 - SFGate

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Elsa Casillas hands out flyers for the unsolved murder of her son at a gun buy back program in the Mission, in San Francisco, Calif., Thursday, August 8, 2013. Guns were exchanged for $100, assault weapons for $200 -- no questions asked. The program was funded by San Francisco Supervisor David Campos' discretionary fund and GunbyGun.org which crowd sourced the money.

Photo: Sarah Rice, Special To The Chronicle

Elsa Casillas hands out flyers for the unsolved murder of her son...

Elsa Casillas hands out flyers for the unsolved murder of her son... Photo-5021052.67888 - SFGate

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San Francisco police department officers check in guns turned over at a gun buy back program in the Mission, in San Francisco, Calif., Thursday, August 8, 2013. Guns were exchanged for $100, assault weapons for $200 -- no questions asked. The program was funded by San Francisco Supervisor David Campos' discretionary fund and GunbyGun.org which crowd sourced the money.

Officer Warren Lee makes sure a gun turned over at a gun buy back program in the Mission is empty of ammunition in San Francisco, Calif., Thursday, August 8, 2013. Guns were exchanged for $100, assault weapons for $200 -- no questions asked. The program was funded by San Francisco Supervisor David Campos' discretionary fund and GunbyGun.org which crowd sourced the money.

Officer Warren Lee hands in a gun turned over by a citizen at a gun buy back program in the Mission in San Francisco, Calif., Thursday, August 8, 2013. Guns were exchanged for $100, assault weapons for $200 -- no questions asked. The program was funded by San Francisco Supervisor David Campos' discretionary fund and GunbyGun.org which crowd sourced the money.

Photo: Sarah Rice, Special To The Chronicle

Officer Warren Lee hands in a gun turned over by a citizen at a gun...

Officer Warren Lee hands in a gun turned over by a citizen at a gun... Photo-5021086.67888 - SFGate

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Officer Hector Basurto puts guns turned over at a gun buy back program into the back of a police van in the Mission, in San Francisco, Calif., Thursday, August 8, 2013. Guns were exchanged for $100, assault weapons for $200 -- no questions asked. The program was funded by San Francisco Supervisor David Campos' discretionary fund and GunbyGun.org which crowd sourced the money.

Officer Warren Lee makes sure a gun turned over at a gun buy back program in the Mission is empty of ammunition in San Francisco, Calif., Thursday, August 8, 2013. Guns were exchanged for $100, assault weapons for $200 -- no questions asked. The program was funded by San Francisco Supervisor David Campos' discretionary fund and GunbyGun.org which crowd sourced the money.

Officer Les Smith checks in guns at a gun buy back program in the Mission in San Francisco, Calif., Thursday, August 8, 2013. Guns were exchanged for $100, assault weapons for $200 -- no questions asked. The program was funded by San Francisco Supervisor David Campos' discretionary fund and GunbyGun.org which crowd sourced the money.

Photo: Sarah Rice, Special To The Chronicle

Officer Les Smith checks in guns at a gun buy back program in the...

Officer Les Smith checks in guns at a gun buy back program in the... Photo-5021081.67888 - SFGate

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Officer Nicholas Shihadeh retrieves a gun turned over by a citizen at a gun buy back program in the Mission in San Francisco, Calif., Thursday, August 8, 2013. Guns were exchanged for $100, assault weapons for $200 -- no questions asked. The program was funded by San Francisco Supervisor David Campos' discretionary fund and GunbyGun.org which crowd sourced the money.

San Francisco police department officers check in guns turned over at a gun buy back program in the Mission, in San Francisco, Calif., Thursday, August 8, 2013. Guns were exchanged for $100, assault weapons for $200 -- no questions asked. The program was funded by San Francisco Supervisor David Campos' discretionary fund and GunbyGun.org which crowd sourced the money.

San Francisco police department officers walk down the line of cars waiting to turn in guns at a gun buy back program in the Mission in San Francisco, Calif., Thursday, August 8, 2013. Guns were exchanged for $100, assault weapons for $200 -- no questions asked. The program was funded by San Francisco Supervisor David Campos' discretionary fund and GunbyGun.org which crowd sourced the money.

Photo: Sarah Rice, Special To The Chronicle

San Francisco police department officers walk down the line of cars...

San Francisco police department officers walk down the line of cars... Photo-5021080.67888 - SFGate

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Officer Les Smith checks in guns at a gun buy back program in the Mission in San Francisco, Calif., Thursday, August 8, 2013. Guns were exchanged for $100, assault weapons for $200 -- no questions asked. The program was funded by San Francisco Supervisor David Campos' discretionary fund and GunbyGun.org which crowd sourced the money.

Photo: Sarah Rice, Special To The Chronicle

Officer Les Smith checks in guns at a gun buy back program in the...

Officer Les Smith checks in guns at a gun buy back program in the... Photo-5021078.67888 - SFGate